Regenerative or recuperative furnaces having melting and fining zones have been commonly employed to manufacture glass. The regenerative or recuperative furnaces, unlike other types of furnaces, employ at least one regenerator or recuperator in operating air-fuel burners. At least one regenerator or recuperator, which may come in many different shapes and sizes, serves to preheat air used in the air-fuel burners. In the regenerator the preheating is generally accomplished by transferring the heat in the existing waste gas from a melting chamber to refractory bricks stacked in a checkerboard fashion. The bricks, in turn, give up their heat to the incoming air which will be used in combusting the fuel. Commonly, the recuperator may consist generally of a double wall tubing in which the off gas from the melting chamber flows in the central tube countercurrent to the air which is passing through the annulus. The performance of the regenerator or recuperator, however, may deteriorate with time because the regenerator or recuperator may be partially plugged or destroyed when it is subject to the waste gas containing chemical contaminants for a long period. The partially plugged or destroyed regenerator or recuperator adversely affects the performance of air-fuel burners, thereby decreasing the glass production rate.
It has been known, therefore, to employ oxygen-fuel burners, in a number of furnaces to supplement the air-fuel burners. U.S. Pat. No. 4,473,388 (Lauwers) issued Sep. 25, 1984 and International Publication WO 82/04246 (Erickson et al) published Dec. 9, 1982, for instance, disclose oxygen-fuel burners installed on the sides of a rectangular glass melting chamber in a particular manner to increase the melting capacity of a furnace. Some unmelted solid glass forming ingredients, however, may be discharged with the molten glass. The presence of unmelted glass forming ingredients in the molten glass product adversely affects the quality of glass products. To enhance the quality of the glass products these unmelted solid glass ingredients need to be prevented from being discharged by employing additional oxygen-fuel auxiliary burners in a manner described in U.S. Pat. Nos. 4,816,056 (Tsai et al) or 3,592,623 (Shepard). The use of the additional oxygen-fuel auxiliary burners, however, may increase the oxygen and fuel consumption and the risk of overheating the roof of a furnace. Moreover, installing a plurality of the oxygen fuel auxiliary burners in a manner described by the above references may be difficult whenever a cross-fired regenerative furnace is utilized due to the location and design of its regenerators.
Accordingly, it is an object of the invention to increase the melting capacity of a regenerative or recuperative furnace and, at the same time, reduce the possibility of unmelted solid glass forming ingredients from discharging with the molten glass, without increasing the risk of overheating the roof of the furnace and without increasing the oxygen and fuel consumption.
It is another object of the invention to maintain a particular glass production rate even when the regenerators are partially plugged or destroyed or are being repaired.
It is yet another object of the invention to install oxygen-fuel auxiliary burners in such a manner to accommodate the restraints imposed by regenerators of a cross-fired or side-fired regenerative furnace.
It is further object of the invention to inhibit the formation of NOx during the glass melting.